Dependent child sponsorships are minimum income exempt - in your undertaking, which you quoted above, you promise to provide for the children for 10 years, or until the child turns 23, whichever comes first. That's a promise you make to Immigration Canada, a commitment to support them, and to pay back the govt if they should ever apply for social assistance. I don't think any of that precludes you from getting any child tax benefits you may be entitled to from the govt, but you should ask a tax attorney.